Impact of time interval between remifentanil and propofol on propofol injection pain

To determine the most effective time interval between remifentanil and propofol (TimeRP) for the prevention of propofol injection pain in association with remifentanil dosage.

Prospective randomized study.

Operating room of a university hospital.

Sixty American Society of Anesthesiologists physical status 1 and 2 patients scheduled for elective surgery under general anesthesia.

Patients were randomly assigned to 1 of 3 groups to receive remifentanil at dosages of 0.25, 0.5, or 0.75 μg/kg over 30 seconds before the injection of 1% propofol 2 mg/kg. TimeRP was defined as the time interval from the initiation of the remifentanil injection to the initiation of the propofol injection. TimeRP for each subsequent patient was determined by the response of the previous patient using an up-and-down sequential allocation method. Injection pain caused by propofol was evaluated using a 4-point scale during the propofol injection.

TimeRP50 was defined as the TimeRP at which propofol injection pain was absent in 50% of patients, and it was estimated using isotonic regression for each dose group.

TimeRP50 was significantly lower in the remifentanil 0.75 μg/kg group (38.6 seconds, 83% confidence interval [CI], 35.6-45.0) than in the 0.5 μg/kg group (65.0 seconds; 83% CI, 52.5-75.0) or the 0.25 μg/kg group (66.6 seconds; 83% CI, 57.1-76.5).

The efficacy of remifentanil pretreatment for preventing propofol injection pain can be influenced by the time interval between remifentanil and propofol as well as the remifentanil dose.